A081880 - OEIS

%I #5 Sep 18 2015 12:56:29

%S 0,2,0,4,2,0,6,8,10,16,42,10,16,42,12,14,32,170,4816,3865642,

%T 2490531345360,16,42,18,20,66,22,80,1066,189392,5978221610,

%U 5956522269711832016,5913359591595499145281505571167104042,5827970276585748074286667660065476529979312208145367609757859954142122960,24,26

%N Triangle read by rows: n-th row gives trajectory of 2n under the map x->(x^2-4)/6, stopping when the next term would be negative or nonintegral.

%H Pierre Abbat, <a href="http://phma.optus.nu/Math/64-100.html">The 64-100 Sequences</a>

%e 8 -> (64-4)/6 = 10 -> (100-4)/6 = 16 -> (256-4)/6 = 42 -> (42^2-4)/6 nonintegral, so stop; thus row 4 is (8, 10, 16, 42).

%e Triangle begins:

%e 0,

%e 2, 0,

%e 4, 2, 0,

%e 6,

%e 8,

%e 10, 16, 42, 10, 16, 42,

%e 12,

%e 14, 32, 170, 4816, 3865642, 2490531345360,

%e 16, 42,

%e 18,

%e 20, 66,

%e 22, 80, 1066, 189392, 5978221610, 5956522269711832016, 5913359591595499145281505571167104042, 5827970276585748074286667660065476529979312208145367609757859954142122960,

%e 24,

%e ...

%K nonn,tabf

%O 0,2

%A _Pierre Abbat_, Apr 12, 2003